A study is proposed of the patient fluoroscopic dose reduction capabilities of controlling the size of the optical iris aperture between the image intensifier optical distributor and the television vidicon. Existing methods for measuring Roentgen-area-product (RAP) using a transmission ion chamber placed over the fluoroscopic x-ray tube will be developed into new time-dose study (TDS) techniques involving the recording of integral RAP value as a function of time throughout the course of the clinical procedures. From this data for a large number of clinical procedures dose reduction will be quantified by the comparison of RAP distributions as a function of iris size, experience of radiologist, and patient physical and clinical parameters. The study will emphasize the double contrast barium enema procedure where high quality images are not always necessary because almost all of the fluoroscopic patient exposure is required for positioning and monitoring rather than diagnosis. It is anticipated that much of the tens of rads of patient entrance dose for this procedure may be eliminated. The proposed study will conclude with a qualitative analysis of any potential utility of operator control of iris size during procedures where both monitoring and diagnosis are involved.